39 lines
1.0 KiB
C++
39 lines
1.0 KiB
C++
template <typename T>
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class lock_free_stack {
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private:
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void increase_head_count(counted_node_ptr& old_counter)
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{
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counted_node_ptr new_counter;
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do {
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new_counter = old_counter;
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++new_counter.external_count;
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} while (!head.compare_exchange_strong(old_counter, new_counter));
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old_counter.external_count = new_counter.external_count;
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}
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public:
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std::shared_ptr<T> pop()
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{
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counted_node_ptr old_head = head.load();
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for (;;) {
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increase_head_count(old_head);
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node* const ptr = old_head.ptr;
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if (!ptr) {
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return std::shared_ptr<T>();
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}
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if (head.compare_exchange_strong(old_head, ptr->next)) {
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std::shared_ptr<T> res;
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res.swap(ptr->data);
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int const count_increase = old_head.external_count - 2;
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if (ptr->internal_count.fetch_add(count_increase) == -count_increase) {
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delete ptr;
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}
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return res;
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}
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else if (ptr->internal_count.fetch_sub(1) == 1) {
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delete ptr;
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}
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}
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}
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};
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